1. Field of the Invention
The present invention relates to a control device for a legged mobile robot, such as a bipedal robot.
2. Description of the Related Art
For a legged mobile robot which moves by the motions of a plurality of legs provided such that the legs extend from a base body, a control technique that allows a desired gait including a desired motion of the robot to be sequentially generated in real time and to control the motion of the robot so as to make the actual gait of the robot follow the desired gait has been proposed by the applicant of the present application in, for example, Japanese Patent No. 3269852, Japanese Patent No. 4246638, and Published PCT International Application WO2002/040224.
To sequentially generate desired motions of the robot in real time while controlling the motion of the robot as described above, it is necessary to supply the information on a floor geometry, which indicates the floor geometry of the environment in which the robot travels, to a device which generates the desired motions. The device which generates the desired motions determines the desired motion by reflecting the information on the floor geometry on the desired motion of the robot.
For example, a desired motion generator determines the motion trajectory of the distal portion of each leg, including an expected landing position or the like of each leg, in a desired motion of the robot on the basis of the supplied floor geometry information.
Basically, the desired motion of the robot should be determined to assure a smooth motion of the robot on an actual floor surface. Hence, it is considered to be desirable that the floor geometry indicated by the floor geometry information used for generating the desired motion always agrees with an actual floor geometry.
In this case, however, the study by the inventor of the present application has revealed that the following inconvenience may occur.
It is assumed that, for example, there is a stepped portion, including a locally projecting portion, around an expected robot travel route, and that the contact between the stepped portion and the distal end of a leg of the robot is not originally expected. In this case, the desired motion generator will determine the motion trajectory of the distal end of the leg of a free leg such that the distal end of the free leg of the robot will not come in contact with the stepped portion. However, there is also a case where the motion trajectory may be a trajectory that passes a position relatively near the stepped portion.
In such a situation, if the actual robot moves completely in accordance with the desired motion, then there will be no contact between the leg of the robot and the stepped portion. However, there is a case where the motion trajectory of the distal end of the free leg relative to the actual floor deviates from the trajectory expected in the desired motion due to a slippage or the like of a supporting leg of the actual robot. In this case, a leg of the robot may come in contact with the stepped portion if the current motion trajectory of the distal end of the leg is maintained as it is.
Further, in this case, the original motion trajectory of the distal end of a leg of the robot is determined on the assumption that there will be no stepped portion on the trajectory. For this reason, if a possibility of contact between the distal end of a free leg and the stepped portion arises due to a slippage of a supporting leg of the actual robot, then changing the motion trajectory of the distal end of the free leg to obviate the possibility of the contact may require a significant change in the motion trajectory. Further, in such a case, it may be inconveniently impossible to actually change the motion trajectory because of restrictions on the dynamics of the robot or the capabilities of actuators.
The present invention has been made with a view toward overcoming the above drawbacks of the prior art, and it is an object of the invention to provide a control device capable of controlling the motions of a robot while generating desired motions that make it possible to properly avoid a predetermined type of stepped portion existing around a travel route of the robot.